Heat and Mass Transfer Operations MCQs 2026

Mass transfer coefficient ky relates flux to

1. A difference in mole fraction or concentration ✓
2. B only pressure drop ✓
3. C only pipe friction ✓
4. D only shaft torque ✓

LMTD in heat exchangers is used when

1. A both fluids at same temperature always ✓
2. B temperature difference varies along exchanger length ✓
3. C only phase change in vacuum ✓
4. D only laminar pipe flow without heat ✓

Overall heat transfer coefficient U accounts for

1. A only radiation always ✓
2. B series resistances of convection, conduction and fouling ✓
3. C only pump head ✓
4. D only reaction rate ✓

Stefan-Boltzmann law for gray body includes emissivity as

1. A multiplier on blackbody emission ✓
2. B divisor on temperature ✓
3. C additive constant to flux ✓
4. D replacement for area ✓

Biot number assesses

1. A inertia versus viscosity ✓
2. B momentum versus diffusion in reactor ✓
3. C internal conduction resistance versus surface convection resistance ✓
4. D pipe roughness only ✓

Fick first law for diffusion is

1. A J = h ΔT ✓
2. B J = k ∇T ✓
3. C J = f ΔP ✓
4. D J = −D dC/dx ✓

Prandtl number Pr equals

1. A hL/k ✓
2. B Cpμ/k ✓
3. C ρvL/μ ✓
4. D k/ρCpL ✓

Nusselt number Nu is defined as

1. A ρvL/μ ✓
2. B μ/ρD ✓
3. C Cpμ/k ✓
4. D hL/k ✓

Newton law of cooling gives convective heat flux as

1. A k ∂T/∂x only ✓
2. B h(T_surface − T_fluid) ✓
3. C σεT⁴ only ✓
4. D ρgh only ✓

Fourier law of heat conduction states

1. A flux proportional to pressure gradient ✓
2. B flux proportional to concentration gradient only ✓
3. C heat flux proportional to negative temperature gradient ✓
4. D flux independent of area ✓